Modern vehicles must control exhaust emissions to meet air quality standards. An exhaust gas oxygen sensor monitors exhaust emissions and inputs exhaust data to an electronic control module that can vary the fuel/air mixture to help keep emissions within the required parameters. As an exhaust gas oxygen sensor ages, its output varies causing exhaust emissions to rise, sometimes above a target level. It is desirable to have a tool for development and production calibration of the electronic control module to identify the exhaust gas oxygen sensor threshold signal degradation that will cause exhaust emissions to exceed the target level. Accordingly, it will be appreciated that it would be highly desirable to have a tool that would mimic the signal of an aged or otherwise degraded exhaust gas oxygen sensor.